where f is the focal length and the power is measured in diopters, or m-1.

Re: What is Power of lens

15/02/2013 - Replied By akansha mittal

Power of lens = 1 / (Focal length in meters)

Re: What is Power of lens

15/02/2013 - Replied By Pyush kumar

the "power of lens" is actually the reflective power,and can't be measured until you go to the eye dr.the test the dr will give you to come up with your eye glass prescription is an objective test,meaning,you are telling the dr which lens you see clearer out of,1 or 2 and so on.if you already wear glasses currently,the power can be read on a device called a lensometer.only a trained pro can read the "power".

Re: What is Power of lens

15/02/2013 - Replied By rajiv tiwari

Optical power (also referred to as dioptric power, refractive power, focusing power, or convergence power) is the degree to which a lens, mirror, or other optical system converges or diverges light. It is equal to the reciprocal of the focal length of the device: P = 1/f. High optical power corresponds to short focal length. The SI unit for optical power is the inverse metre (m-1), which is commonly called the dioptre.

Re: What is Power of lens

21/09/2012 - Replied By Gaurav Gautam

As light rays pass through a lens with power, the rays are bent or refracted. In a lens with a plus power, the light rays converge or are refracted toward one another. The point at which the light rays converge is called the focal point and in a plus lens, is behind the lens surface. In a lens with a minus power, the light rays diverge or are refracted away from one another. If these rays are extrapolated or traced back toward the light source, the lines will converge and form a focal point in front of the lens surface.

The lens power is relative to the focal distance or the distance between the focal point and the lens. More specifically, lens power is the reciprocal of the focal distance in meters. Lens power is expressed in diopters (D).

Power = 1 / Focal Distance

As explained above, if the light rays converge, the focal distance is expressed with a positive value resulting in a positive or plus power. If the light rays diverge, the focal distance is expressed with a negative value resulting in a negative or minus power.

Example:

Light rays pass through a lens and converge 0.50 m from the lens What is the power of the lens?

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